This invention relates in general to clutches and in particular to an internally assisted friction clutch which normally relies upon the forces generated by the engagement and assister springs for centering and rotating the release sleeve with the cover, and which further includes one or more cooperating protrusions and recesses formed on the release sleeve and the cover in order to prevent excessive relative rotation from occurring under extreme operating conditions.
Clutches are well known devices which are used to selectively connect a source of rotational power, such as the crankshaft of an engine, to a driven mechanism, such as a transmission. Typically, a cover of the clutch is connected to a flywheel carried on the end of the engine crankshaft for rotation therewith. Between the flywheel and the clutch cover, a pressure plate is disposed. The pressure plate is connected for rotation with the flywheel and the cover, but is permitted to move axially relative thereto. A driven disc assembly is disposed within the clutch between the pressure plate and the flywheel. The driven disc assembly is carried on an output shaft of the clutch, which is also the input shaft to the transmission.
When the pressure plate is moved toward the flywheel, the driven disc assembly is frictionally engaged therebetween so as to cause the output shaft of the clutch to rotate with the flywheel, the cover, and the pressure plate. In this manner, the clutch is engaged to transmit power from the engine to the transmission to drive the vehicle. When the pressure plate is moved away from the flywheel, the driven disc assembly is released from such frictional engagement so as to disconnect this driving connection. The clutch is typically disengaged to permit a gear shifting operation to occur within the transmission.
A release assembly is provided for selectively moving the pressure plate back and forth in the axial direction, so as to engage and disengage the clutch as desired. The release assembly includes a generally cylindrical release sleeve which is disposed about the output shaft of the clutch. The forward end of the release sleeve extends within the clutch. A plurality of levers or similar actuating means is typically connected between the release sleeve and the cover. Portions of the levers abut the pressure plate such that movement of the release sleeve causes corresponding movement of the pressure plate. Engagement springs are typically mounted between the release sleeve and the cover for urging the release sleeve and the pressure plate toward their engaged positions. The rearward end of the release sleeve extends through a central opening formed through the cover. A bearing assembly is mounted on the rearward end of the release sleeve. A manually operable shift lever is connected to the bearing assembly for effecting movement of the release sleeve and, therefore, the pressure plate.
More recently, clutches have also been provided with a plurality of assister springs mounted between the release sleeve and the cover. The assister springs extend generally radially between the cover and the release sleeve when the clutch is engaged, thus exerting little or no axial force on the release sleeve. However, when the release sleeve is moved from its engaged position to its disengaged position, the assister springs are moved to an angular orientation. Consequently, the assister springs exert some axial force tending to move the release sleeve to its disengaged position.
Thus, it can be seen that the release sleeve rotates with the cover during use. Relative rotation between the release sleeve and the cover is undesirable because it causes wear on the levers connected therebetween. Also, excessive relative rotation can cause the engagement springs to be twisted off of their seats on the release sleeve and the cover, thus damaging the clutch. In order to prevent such relative rotation, some prior clutches have been provided with splines formed on the release sleeve which cooperate with corresponding splines formed on the cover. Other prior clutches have been provided with enlarged protrusions on the inner surface of the cover which extend into slots formed on an enlarged portion of the release sleeve.
In both of these prior clutch structures, the spacing between the engaging portions of the cover and the release sleeve is very close. In other words, only a very small amount of relative rotation is permitted before these portions engage one another to prevent further relative rotation. Unfortunately, the release sleeve constantly exerts a certain amount of drag relative to the cover because of friction in the bearing assembly. As a result of this drag, the engaging portions of these prior clutches frequently contact one another during use, even under low torque and speed operating conditions.
Such engagement, while desirable from the standpoint of preventing relative rotation, is undesirable because it causes wear between the engaging portions. Such engagement is also undesirable because it tends to resist axial movement of the release sleeve between the engaged and disengaged positions, thus decreasing the effective engagement force generated by the engagement springs and increasing the amount of force required to move the release sleeve toward the disengaged position. Thus, it would be desirable to provide a clutch structure which prevents relative rotation between the cover and the release sleeve without frequently causing undesirable frictional engagement therebetween.